Preparation of aryl monocarboxylic acids



Sept. 9, 1952 J. 1 DARRAGH Erm.

PREPARATION oF ARYL MoNo-cAmsoxYLIc ACIDS 2 SHEETS-SHEET l Original Filed Oct. 4, 1947 Sept. 9, 1952 J. L. DARRAGH ETAL 2,510,211

PREPARATION oF ARYL MoNo-CARoxYLIc ACIDS original Filed oct. 4, 1947 2 SHEETS- SHEET 2 mm2/512m zoom III. oom o9. oom oo@l m o l.. 2 mmsbmmzml.. oom can oo# oom mm mm .d d w 3 mi@ N l* a I^.

M m D H l mw n wm amv anozNaa .0131A 7. wow

INVENTORS l JOHN 1 DARRAGH ROBERT J. MILLER BY QQ M fi-gygw ATTOR'NEYS Patented Sept. 9, 1952 PREPARATION oF ARrLMoNocAREoXYLro-Acrns .lohn L. Darragh and Robert J.. Miller, Berkeley, Calif., assignors to California Research Corpo-` ration, San Francisco, Calif., a corporation of Delaware Original application October 4, 1947, Serial No.

777,970. Divided and this application December 22, 1950, Serial No. ,202,384

5 claims. (creto-524) This invention relates to the preparation of aryl carboxylic acids in which a carboxyl group preferably is directly attached to the aromatic nucleus and involves the production of such aryl carboxylic acids from alkyl ar-omatic hydrocarbons and preferably from polymethyl-substituted aromatic hydrocarbons. Moreparticularly, the

invention relatesto a process for producing mononuclear. polycarboxylic acids, and in its preferred embodiment comprises a process for-preparing isomeric phthalic acids, such asthe terephthalic isomer. f

Y Known methods for producing isomeric phthalic acids, such as terephthalidhave utilized indirect chemical syntheses Which result in costs so high asto be prohibitive for large scale production. Certain more direct methods such as oxidation of para-xylene `With potassium permanganate or chromic acid require consumption of relatively expensive chemical reagents and likewise involve excessive costs.

An object of this invention is to provide a new and improved process for the production of aryl carboxylic acids and one which is of special advantage for preparing isomeric phthalic acids. Another obj ect is to furnish an improved method for the synthesis of terephthalic acid,

Additionally, an object is to synthesize mononuclear aryl polycarboxylic acids with low cost chemical reagents.

Another object is to produce terephthalic acid by a process which involves oxidation with caustic alkali. Further, an object is to provide a process capable of enhancing yields of carboxylic acids in the caustic oxidation of aryl methyl chlorides.

Other objects and advantages of the invention will beapparent from the drawing and the following detailed disclosure. .d

'In accordance with this invention aryl carboxylic acids, particularly mono-nuclearl aryl polycarboxylic acids, are obtained by formation of polyalkyl aromatic chlorides in which a chlo rine atom is attached to a primary alkyl carbon atom, and conversion of such chlorides to car boxylic `acids by reactions involving oxidation with aqueous caustic alkali. Preferably, the chlorinated primary alkyl carbon atom is attached directly to a benzene nucleus, as in chlorides of para-xylene:

creol emol i ouch .CH ch ci H3 emol ons V013201 p-xylyl chloride p-xylylene `p-xylal-chloride E-chloromethyl dichloride enza'l chloride However, the process is applicable to compounds such as omomci omcmci 01310151201 CH@ croci cHl-cmcl CHzCl CH'LICI on ou 1 /CH3 om on CHzCl and their homologs. Corresponding derivatives of naphthalene and anthracene also may be utilized.

Briefly described, a process embodying the present invention utilizes a combination of process steps involving:

(1) Formation of an aryl substituted primary alkyl chloride such as xylyl chloride xylal chloride (CHaCsHiCHClz), xylylene dichloride (ClC'I-IzCsHfiCHgCl), or mixtures thereof, either by chlorination of xylenc Aor by chloromethylation of toluene or both;

(2) `Separation of at least a xylylenedichloride fraction from the chlorinated reaction mixture;

(3) Conversion ofthe separated xylene chlorides to corresponding carboxylic acids by hydrolysis "and oxidation with aqueous caustic alkali;

(4) Chlorination of Aat least a part of theresulting toluic acids to corresponding chloromethyl benzoic acids, .and

(5) Conversion of chloromethyl benzoic acids principal present application in the manufactureV of terephthalic and/or isophthalic acids, the invention and process will be illustrated hereinafter by reference to the production of these iso'- merio phthalic acids from the xylenes and/or toluene. Special emphasis is herein given to the production of terephthalic acid from paraxylene.

In the drawing, Fig. 1, is a flow sheet illustrating in block diagram a process for converting para-xylene to terephthalic acid or for obtaining a. mixture of phthalic acids from toluene or forV producing mixed phthalic with or without benzoic acid from Xylene and toluene.

Fig. 2 is a graphical showing Variation with temperature of yield of terephthalic acid and terephthalic content of acids from caustic oxidation of chloromethyl benzoic acid.

Fig. 3 is a similar graph showing effect of temperature on yield of benzoic acid from benzyl chloride.

Reference to the drawing will reveal that a xylene fraction such as para-xylene is introduced by Way of feed line ID to a chlorination zone II where chlorine is introduced. into the methyl side chains. The chlorination reaction is conducted under conditions which favor side chain chlorination and may result in the following reactions:

CH3A cHioi heat *l* C12 HCl iight CH3 CH2 (p-xylyl chloride) CHZC] CHZC] heat -I- C12 HC1 light Y CHS oHzCi I (p-xylylene dichloride) CHzCl CEClg heat .C12 HC1 -ll .light CH3 CH3 (p-xyla-l chloride) Tri" and poly-chlorinated compounds also may be formed. If minor amounts of ring chlorination 'occurs,`the subsequent process steps still yield the desired compounds. Y The mixture of chlorinated 'products then passes as indicated byline I2 to a separation zone I3and, as here shown,` three fractions of' chlorinatedk xylenes are obtained. Any suitable method of separation, such as distillation under relatively high vacuum (to minimize decompositionv of the chlorides), may be used. vWhen the hydrocarbon feed is paraxylene, a para-'xylyl chloride fraction, a paraxylal chloride fraction and a para-xylylene dichloride fraction are conducted as shown by lines I4, I6 and II, respectively, to further processing units. If benzyl chloride is formed from any toluene present in the xylene feed, this chloride is removed by Way of line 29. Lower boiling fractions, such as unchlorinated hydrocarbons, may be removed through outlet 30 and high boiling compounds are withdrawn as indicated by line 35.

The para-xylyl chloride fraction from line I4 is converted to para-toluic acid by reactions involving hydrolysis and oxidation of the hydrolyzed product to toluic acid.

CH Clz CH; CH3

CHO

After being converted vfrom the salt to the free acid the para-toluic acid from zones I9 and 2| next is subjected to side-chain chlorination to form chloromethyl benzoic acids by the reactions:

(|1113 cHZci O +012 +Ho1 I l oooH oooH (Molten) Minor chlorination in the ring is not. precluded.

Although the lpara-toluic acid maybe chlorinated While dissolved in solvents such as carbon tetrachloride, better results have :been obtained by direct chlorination of the molten acid, for

i example, at temperatures of from 190 C. to

The foregoing conversion to chloromethyl benzoic acid is effected in reaction zone 22 from which the chlorinated products are conveyed as shown by line 23 to reaction zone 24 for conversion to terephthalic acid. In this reaction zone the chloromethyl groups are hydrolyzed and then oxidized by aqueous caustic alkali to a carboxyl group, thereby yielding terephthalic acid by the following reactions:

` COONA CHQOH COONa COONa COOH CHQCI COONa CHzOH Corresponding reactions occur with dichloromethyl toluic and trichloromethyl toluic acids.

The reaction mixture containing terephthalic acid passes to product recovery zone 26. Any suitable method of recovery and purification may be used, for example, acidification, crystallization and washing with solvents.

When and if a mixtureof xylenes is fed to chlorination zone H, a corresponding mixture of ortho, meta and para-xylene chloride isomers Will be obtained. The product` Will therefore be mixed isomeric phthalic acids; but, if desired, a separation betWeen'para-toluic acid on the one hand and meta and ortho-toulic acids on `the other hand may be effected, as `by 4distillation. Two different phthalic acid products, namely, a terephthalic acid and arnixture of `ortho andmeta-phthalic acid, niaythen be produced from the tWo separated toluic acid fractions. After such a separation (not shown in flow sheet), the mixed ortho and meta-toluic acid fraction may be Withdrawn as indicated by line 21 from caustic oxidation zone I 9. The resulting para-toluic passes to zone 22 for chlorination as shown. The xylylene dichlorides may be separated in suitable fashion.--

Thus, because of its high melting point `theparaxylylene dichloride may be separated by crystallization. The ortho` and meta-isomers maylbe separated from 'each other by fractional 'distillation, preferably under vacuum to` avoid 'decomposition.A i q. i Y m- Toluene which may be contained in the mixed xylene feed or separately introduced `by 'Way of valve-controlled line `273 will `be chlorinated in zonell to form benzyl chloride Which iscon.- ducted to separation Zone1l3 and Withdrawn therefrom as ai benzyl chloride fraction indicated by line 23. The benzyl chloride fractionuis converted to a rnixture of xylylene dichlorides by chlorornethylationin zone- 3|;Y `The xylylene dichloride product is hydrolyzed to thecorresponding glycol in zone 32 andthe glycol converted to ,isomeric` phthalic acids byioxidation with aqueous caustic alkali in zoneS.

In order to augment the supply of mixed xylene chlorides and provide a supplemental `production of toluic acids and vchloro-toluic acids, toluene admitted by Way `of inlet line 34 may be converted to xylyl chloride by chloromethylation in reaction `zone 35. The hydrogen chloride formed in xylene chlorination zone.- II together with formaldehyde is utilized as shown to effectthe chloromethylation reaction. A mixture of ortho, meta and para-xylyl chlorides from reaction zonei -is passed. byavay` of line 3l to separation'zone 3B. If desired, the xylyl chloridesl may be .fractionatedy and a `puriied para-xylyl chloride fraction removed fromfseparation zoned by Way of line lili.V When a mixed xylene hydrocarbon feed is used for Zone .I |only mixed chlorides need be separated in zone 38. Hydrolysis to methyl benzyl alcohol in reaction zone i8 and conversion to a mixture of toluic acids in reaction zone I9 is effected as previouslydisclosed. If and When it is'desired to synthesize a relatively pure terephthalic acid, the mixed toluic acids are fractionated to separate a paratoluic product and leave a mixed ortho and metatoluic acid fraction as previously disclosed. The para-toluic acid fraction Will then be'passed to chlorination zone 22 for Vconversion `toi parafchloromethyl benzoic acid. The chloromethyl benzoic acid then passes as shown by line` 2,3 to caustic oxidation zone 24 Where it is converted to terephthalic acid in the manner hereinbefore disclosed. The process of this invention and suitable modes of operation Will be readily apparent in the light of the following illustrative data and examples. y f l i I. I

In small scale operations, the :chlorination reaction of zone `I I was `carried out, in glass reactor equipped With a sintered glass plate at thebottom through which, gaseous chlorine `was fed: The reactor `when used-,for continuous chlorination Was `provided `With `an inlet-line` at the bottom,

` .throughwhichthe hydrocarbonfeed entered the reactor and an outlet line nearthe `topfor, removal of reaction Amixture at the :same :ratefas `hydrocarbonentered the reaction `zone.` Reaction temperatures were taken by ia-xthermocouple extending into the` reactioniliqui'd. The reactor was topped by a `Water-cooled condenser through which `exit "gases were `removed and absorbed in aqueous caustic. ."llacuumvdistillations utilized for separating the xylene chlorides were carried out in distillation columns packed with glass helices .and equipped 'With an ele'ctrically heated jacket? Liquid constituents-of the reaction mixtures were removed .through anordi'- nary Water-cooled head. Para-xylylene dichloride and other high melting constituents were taken olf the fractionating column through a special head surrounded by a glass jacket containing boiling toluene to prevent solidication in the lines prior to reaching the storage receiver.

Chlorination in batch operation can be effected in the presence of light at approximately 95 C'. This temperature may be varied from 40 to 130 C., for example. When theoretical quantities of chlorine necessary t form a xylylene dichloride were passed into the reaction mixture, some dehydrohalogenation occured both during chlorination and upon distillation of the chlorinated product under vacuum at 3-8 mm. mercury pressure. Continuous chlorination was carried out at about 95 C.' in the presence of light with greatly improved results. Para-xylene and chlorine were fed to the feactor at constant rates and excellent chlorine utilization obtained. Steady state compositions were obtained for each feed ratio in continuous chlorination by taking samples from the continuously withdrawn chlorinated product and analyzing for chlorine content. When chlorine content became constant, the reactor was assumed to be under steady state operation. In the data here given, chlorine contents were measured by saponication numbers.

Because of the many possible products, complete analysis of the chlorinated mixtures was not made, but several of the retained samples were analyzed by distillation at reduced pressure to give compositions of typical chlorinated reaction mixtures.

TABLE I Distillatz'on analysis of chlorinated 12b-mylene DistiuatiQnNo 1 l 2 s 4 From the results of the foregoing distillations, it will be seen that as the chlorine to para-xylene feed ratios are increased Vthe yield of paraxylylene dichloride increases.

A large batch of the reaction mixture of chlorinated compounds was treated for separation as follows: The chlorinated mixture was cooled in anice bath and the crystals formed were filtered ofl. The filtrate Was then charged to a still and unreacted para-xylene and paraxylyl chloride removed under vacuum. The still bottoms were dissolved in about half their volume of chloroform and the resulting solution cooled in an ice bath where additional crystals were recovered and combined with those rst separated. These crystals, after purification by recrystallization from chloroform, were identilied as para-xylylene dichloride by chlorine content, melting point and hydrolysis to the paraxylylene glycol derivative.

rThe mother liquor from the foregoing chloroform crystallization was concentrated to 50% of its volumeA and again cooled in an ice bath. A

Conversion of .rylyl chloride A preferred mode of operation involves simultaneous hydrolysis and oxidation of xylyl chloride to the corresponding toluic acid'at 300 C. to 400 C. (M5-'750 FJ. The overall reaction may be written:

*CHZCI heat COONa NaCl -I- 2R20 However, it may be effected in two stages:

-1- ZHZO CH3 CH3 A single stage operation presently is regarded as most desirable. The reaction may be effected by agitation in a rocker type autoclave under the following conditions:

Time, hours 1 Temperature, C. 371 Caustic concentration, per cent 8 NaOH, moles 2 Xylyl chloride, moles 1 Yield of toluic acid (moles per mole of xylyl chloride) .85

Xylal chloride conversion Xylal chloride is converted to the corresponding toluic acid by hydrolysis and oxidation preferably at 300 C. to 400 C. (S75-'750 FJ. These reactions may be eifected by agitation in rocker type autoclave as follows:

Time, hours 1 Temperature, C. 371 Caustic concentration, per cent 10.9 NaOH, moles 3 Xylal chloride, moles 1 Yield of toluic acid, moles per mole of xylal chloride .91

Conversion of ylylene dichlorz'de In small scale runs for this stage of the process reactions were carried out in a rocking autoclave capable of withstanding pressures up to 15,000 pounds per square inch gauge and constructed entirely of Monel metal. The head of the vessel was tted with a thermocouple, a safety valve, vent, a pressure gauge and a sample valve. Heat was supplied through strip heaters located in the yields a' terephthalic` acid product containing impurities. Yields and impurity contents are` illustratedby the following table oi' data:

ACIK

autoclave casing. The whole assembly was agi- @H201 CH2OH` ltateol by rocking in a vertical plane with a maximum deviation from the horizontal 0f 30 and at .1 30H ma@ a rate of 78 cycles per minute. i

The desired material was charged to the auto- C1 H clave together with a predetermined amount of 2 C 20H caustic soda, water and the oxidizing agent when p`xy1y1enedmhlmde pxylylene glycol one was used. The vessel was lock-closed, vplaced CHH COONa in a shaker casing, and if a gaseous oxidizing agent such as air or oxygen was to be used, it was zNeoa l-e l Y -l-.lm charged at this time through the sample valve. 20 The amount of oxidizing agent was calculated CHQOH UOONafrom the total pressure and known free-space in the vessel. terephthalic acid Heat was turned on and shaking started. After reaching reaction temperature, ythe mixture was 1n any @Vent it has been GllDd that telephallowed to react for one hour while controlling than@ 'acid Can be prepared lOm Pam-Xylllene the temperature to maintain it substantially conglyCOl by subjecting the glycol to caustic oxistant, At the end 0f one hour reactgn time (exdation at 371 C. (700D F.) for one hour as in the elusive of heating and cooling periods), shaking COHVGFSOH 0f parta-Xylylolle dClllOldG- The was Stopped, heat turned Off and the apparatus product from the caustic oxidation of paraallowed to cool overnight. Upon removal of the Xylylel@ gli/CO1 Contained a neutral product, Daraeooled reaction mixture from the autoclave, it was tOlUlC acid, and telephthol @Cid Substantially aS ultered to remove dirt and traces ofinsoluble byin the previous preparation from para-xy1v1eno products and next acidiiied to a pHof 3.0 with flClllOlfle The Xylllell@ fllCOl Was Obtained HC1 to convert the salts back to free acid which 35 for this reaction by hydrolysis in a dilute Water forms a precipitate. The precipitated acid was solution at Areflux. temperature followed by exrecovered by filtration, washed free of chloride tlaCtlOIl With ether t0 IGCOVST the glycol from ion,v dried and weighed. A. sample of the dried the aqueous medium. Aproduct was dissolved in a. standard base solution, Important variables woronvosteatod to doterback-titrated potentiometrically with standard 40 mln@ 'thell @GGtS lllJGl the fOlBOng Caustic acid and the acid number obtained. Yield was oxidation retwtions.` Among the factors investicalculated from these data. gated Weie 'Elect ofA concentration of the xylene Pure para-xylylene dichloride when reacted chloride in the caustic, effect of concentration of with four ormore `mols of caustic soda per mol caustic and of excess proportions of the caustic ofthe dichloride at3711 C. (700 FJ for one hour 45 Solution on the product. effector" time and temperature of reaction," and effect of oxidizing reagents. Each of these factors is discussed hereinbelow.

The by-product on which approximate percentages are given above is a neutral, pasty material `insoluble in aqueous caustic. `The acid numbers shown the foregoing table'swere obtained on the crude chloride-free lacidicreaction products. 'Acid-numbers can` be raised to from about )500-512"Y in all cases `by.recrystallizati'on from water. The signicarice of1 acid numbers is illustrated by` theoretical acid numbers `as follows;V i H Toluic acid 4 l 11 4112 Terephthaliciacid 1. 672

Eect of concentratio'on conversion of xylylene dichloride A decrease.intconcentration of the xylylene dichloride increases'the acid number ofthe product and reduces the amount of neutral lay-product. The `weight yield of the `product remains substantially constant and the concentration as well as the amount of excess caustic over theoretioal appeared to have'no effecten the `product within the limits investigated. `The-follow,- ing series of datainywhich the reactions were TABLE III yields of nearly pure terephthalic acid have been obtained by intimately contacting the reaction Oxidation of varying concentrations of xylylenc dichloride to terephthalic acid Wei ht Weight Mols M 01S conc. Percent Perce/t of Yield of Acid No. ('ylylene NaOH NaQH Conv. Byrod. Acids of Prlodilc;

ichloride Used Solution, Based'on Based on Based on mg. Charged Percent Chloride Ch Charge, per Gram arge Percent 0. 50 2. 0 8. 1 100 1. 0 65 452 O. 50 2. 0 8. 7 100 1. 7 64 427 0. 2. 0 8. 1 100 trace 91 520 0. 02 2. 0 8. l 100 trace 69 577 0. 02 2. 0 8. l 100 trace (i7 570 0. 02 0. 08 0. 4 100 trace 63 572 Eect of temperature, time, and pressure on aylylcne dichloride conversion A temperature between 31E-371 C.. (GOO-700 TABLE v Caustic oxidation of :11g/igiene dichioride in the presence of added oxidizing agents F.) yields a product of a fairly constant acid number. As temperatures increased above 371 (70.0 F.) or reaction times are prolonged, or both., the yield of total acid drops oil. Thus, it appears that about 315 C. (600 F.) is as high a, temperature as is necessary and that reaction times in excess of one hour achieve little or no benefit. However, the process is operative at temperatures of from 25.0 C. to 400 C. M80-750 Conc. Percent Mols Xy- Mols o Acid N o. Terephlylene Di Igl lggnH Available Ofe'ficl Yilglof Acids mgs. tha-11e in chloride Used Per" Used Oxygen Oxygen Acids KOH per Prod. Charged cent Charged Charged gram Percent 0. 02 0. 915 3. 9 NaOCl 0. 01 50 88 623 81 0. 02 0. 90 3. 8 NaOCl 02 100 94 G73 100 02 l. 0 4. 2 Air 0. 08 400 88 647 100 25 1` 87 7. 0 O2 0. 49 200 99 668 98 All of the above runs were made at 315 C. v (600 F.) and one hour reaction time at this temperature.

Conversion of toluic acids E). Illustrative data are given in the following methyl group and caustic alkali oxidation of the table: resulting chloromethyl benzoic acid (iz-chloro- TABLE IV Oxidation of :rylyiene dichZoride-oariable time and temperature weight Mois Mols conc. pevglgltf ".Yield Acid No. Xylylene NaOH NaOH Time, Tem B Pr0d Acids Product Dlhlorie Used 1)Solnt Hours F. ucBased Bied on mg. (lOH al' e el'CD alg, DGI ram g on Charge Percent 0.02 1. o 4. 2 1. 0 55o 14 37 507 o. o2 1. o 4. 2 1. o too None 77 584 o. o2 1. o 4. 2 1. o 65o None 75 57o o. o2 1. u 4. 2 4. o 65o. None 75 579 o. 02 2. s s. 1 4. 7 5 70.0- None 4a 615 0.02 1.o 4.2 1.oy 75o None 23 573 0,02 1.0, 4.,@ 4.25v 750 None None l Pressure is not critical except that it should be suficient to maintain the aqueous caustic in liquid phase.

Effect of oxidizing agents on conversion of yiy- Iene dichioride It has been found that use of an oxidizing agent, such as air, achieves a marked improvement in yields and purity of the terephthalic acid product.

Each of these stages will be In fact, substantially theoretical bath and leading to the bottom of the reactor.

l13 Exit gases fromA the reaction mixture pass through a side-arm to a condenser. The toluic acids tend to sublime and plug air cqndensers. To alleviate this tendency an oil heated conperature decreased dehydrohalogenation and at the same time increased chlorine utilization as well as the chlorine content of the product.. The extent to which the temperature may be lowered denser was attached `to the reactorand `an ai-r-l 5 Vis limited by the fluidity of the reaction mixture cooled condenser in turn attached to the outlet which contains some high melting components. of the oil heated condenser. Exit gases, thus, From the data in Table VI, it also appears that 'rst passed through the oil condenser Where a oxidation `occurs under the chlorination condimajor proportion of any sublimed acids were tions. While some ofthe para-toluic acid charge condensed, meltedand returned to the reactor. 10 stocks contain terephthalic acid, the amount The remaining gases next flowed to the air contherein is nsufcient to account for the high acid denser and were led to a caustic absorberlfor number of the products. Extraction of the chlo- `extracting HC1 and residual acidic products carrinated products with 190 proof alcohol (in which ried thereby. 'r terephthalic acid is insoluble) yielded an alco- `Although para-toluic acid, for example, may be L hol soluble portion and an alcohol insoluble porchlorinated in boiling carbon tetrachloride in tion having acid numbers of 366 and 522, respecthe presence of light, direct chlorination of tively. Accordingly/4, it is believed that the chlomolten toluic acids yields better results.` The rine serves as an oxidizing agent to convert a Vtoluic acid is charged to the reactor, melted, n portion of the para-toluic acid to terephthalic heated to` the desired temperatureand thereo acid by anoxidation reaction which is presently after contacted `With gaseous chlorine under `connot understood. e' u' `stant agitation. `'Il'emperatures of froml90 C. 'O11 Cumprliug .Sample 10 with Samples 8 and, to 270 C. are suitable4 conditions. While chioltarnears that removal of impurities fromth'e rination of para-toluic acid to form para-methyl K N crt. ve toluic acid by Caustic purification or distilbenzoic acid is a, preferred aspect 0f the invern. D lation achieves substantial improvements in chlotion since a main objective is to produce terephrine utilization, and in yields and purity ofproduct. thalic acid, it Was found that all three isomers Conversion of para chloromethi/Z bezo'ic oftoluic acid will undergo direct side-chainchlo- @CML-The parachloroinethyl toluic acid desirrination in the molten state. Ortho toluic` acid ably is Colli/@lied t0 terephthalicacid in'a single gave a 13.7% chlorinecontaining product, for "0 Stege caustic oxidation process by contacting example; and two runs with meta-toluic acid with aqueous Caustic at 15o-400 C.. for example yielded products containing 16.8 and 19.1 chloat 315 C. (606 E). The following examples are rine, respectively. Various runs made with paraillustrative and show that chlorine content of the toluic acid and data on results obtained are .w feed wlthin the ranges tested has n0 profound given in Table VI; 30. effect upon the acid number of the product. A

" TABLE VI Chlorznation of p-toluic acid i Per Cent 1Grn.of Per PerCentof Gm. Pe C t s '1 AcidNdof" i Tcre- Tem i C12 used Cent Reacted Prod. Chrlorlllle Acid No. agg) e Description 0l Charge Charce mg. phthalic o Op' per gm. of C12 Cl? which per b mg. KOH KOH/gm. Acidin Toluic `Re` dehydro- Gm. of W ht per gm.

Charge Acid acted halogenated Toluic eg p-toluic acid (C. P.) 412 0 1.19 375 pt0luic acid Laboratory Prep. M. P. 414 8 246-252 1. O7 14. 2 450 17e-180s o. p-toluic acid, laboratory Prep. M. I. 414 G. 8 246-252 1. O7 13. 0 447 17s-1so.5 o. p-toluic acid, LaboratoryV Prep. 422 3.8 246-252 .668 68 34 1.17 13.2 `446 1v1. P. 177 220o. i -4 p-toluic acid, Laboratory Prep. '414 `.8 252 .884 73 v44 1 10 16.4 480 M. P;17s-1s0.5 o. 1w 1 i 1 1 i p-toluic acid, Laboratory Prep i 426` 5.3 246-252 .922 66 56 .96 N 14.4 461 pltoluic acid, from Pilot Plant, '445 12.5 246-252 .S38 79 55 1.08 13.7 520 Caustic purified p-tuluic acid, from Pilot riant, 447 13.3 232-241 .982 s2 52 1.00 17.7 502 Caustic purified A 9 p-toluie acid, from Print Plant, 447 13.3. 232-241 .032 73 55 1.11 14.1 500 Calstic purified, air and chlorine use 10 p-roiuic acid, from Pilot Plant, 430 13.0 232-241 882 so 60 .98 i 12.4 516 Steam stripped, containing about 2% polymer i Attention is directed to the fact that in Table large excess of oxygen diminished the Weight IV, Example No. 8 shows that reduction of tem- `yield of product. l 1

, TABLE VII Orz'dar'ion of chlorinated p-toluzcaczfd in `caustic A soda ut high-temperature e Product i Chloriuated Chlorine Moles Moles NaOH Tolu1cAc1d 1n Charge, Oxygen Yield of To- RIDING Charged, Percent of lsg Pselclt Charged tal Acids, Percent lggef Acid No.

1 u Grams Theory 1 (as air) Percent by p-toluic thallc mgs, KOH Weight of Acid A id per Gram i Charge C i 5.10 l 78 1.0 4.2 0.030 94 i 2e 74 1 -605 5.0 1 74 1.0 4.2 0. 003 s2 23 77 614 5.0 es 1.0 4.2 0.040 0s 10 90 04s 5.0 e2 110 4.2 0.040 04 1s 82 Y 034 5.0 02 1.0 4.2 0.040V 94 13` 87 040 5.0 00 1.0 4.2 0.109 70 `10 90 64s The effect of different variables on the single stage conversion of para-chloromethyl benzoic excess of caustic soda. Illustrative data are given in Table IX:

TABLE 1X Caustic oxidation of a-ctloro-p-toluic acid Product4 Chloro Chlorine Cone Y toluic Mols Mols Sample 1n Charge, NaOH Yield o Y No. Clgud Percent lgs?? Soln, giig Total Acids Percent. Prlt Ncgs aigus of Theory Percent g Percent by p-toluic hihahc KO'H pei; t Weight of Acid P Acid Gram Charge i Y Y 57. 9 65 1. 5 5. e 0,35 95 14 se 63s 69. 5 66 1. 5 5. 6 0.37 93 8 92 Y 654 103 85 2. (l 9. 9 0. 60 95 4 96 662 80.0 68 1. 5 8. l 0.50 98 3 97 666 86. 6 59 1. 6 8. 4 0. 53 87 19 81 1 625 1 This experiment was made on a chlorinated crude toluic acid.

vacid was investigated.v

Effect of temperature on conversion of chloromethyl benaoic acid-Effect of temperature is decided in altering yields of total acids as well as per cent terephthalic acid in the reaction product. The effect of changes in temperature on total weight of acids and on the percentage of terephthalic in the acid reaction products is illustrated graphically in Fig. 2 based on the data of Table VIII. Yield drops rapidly below 200 C. (400 F.) and little benet is apparent above 315 C. (600 111.). Temperatures of l50-400 C. are operative. l The data in Table VIII were ob- TABLE X Use of oxygen in caustic oxidation of a-chioro-ptoluic acid to tcrephthalic acid Product Chlorine Chlororotomic m Mois NaOH M018 Yield 0i Sample Acid Charge NaOH soi'n Oxygen Total Percent No. Charged Percent Used Percent Charged Acids Percent Terepib Acid No.

Grams I (as au) Percent by p'tolulc thalic mgs' KOH Theory Weight 0i Acid Acid per Gram Charge :tained in small scale runs in which reaction time was one hour and charge stock contained 78% of theoretical chlorine for para-chloromethyl benzoic acid.

TABLE VIII Ortho-chloromethyl toluic acid and metachloromethyl toluic acid have been converted to their corresponding phthalic acids by caustic oxidation at temperatures within the range of Effect of temperature on. caustic oxidation of u.-chZoro-p-tolaic acid Product Chkiinqted M 1 N on Moles W hi p- 4o ulc o es a eig Y- Sipe Acid NaOH sol'n, gigigl Tliilp- Yield of Percent Percent Acid No Charged, Used Percent (as agr) Acids Toi Tereph- OH rams Percent .lc thalic mgS'G Y byvveigni AC1 Acid Per fam of Charge Eect of concentrations on conversion of chloromethyl benaoic acid-The foregoing runs were performed With the chlorinated toluic acids present in dilute solution and with ahigh molarex-V cess of caustic acid. Additional tests revealedY 15G-400 C., e. g. at 315 C. (600 R), for a reaction period oi one hour in a manner similar to the foregoing examples with para-chloro- .methyl toluic acid. The invention and condition for reaction as herein disclosed is applicable to the orthoand meta-isomers as well as to the para-product.

Efect of Caustic Concentration.-Relatively dilutesolutions of `caustic 'alkali in Water areipreeI the rangeof from-4` to 10% by Weightof` caustic soda and it was evident.` that higher concentrationsasf Well as somewhat. more dilute solutions are t operative.

t A Conversions by chloromethylation ,Utilizationof by-product HC1 by chloromethyl-` lCTI catusticx` oxidation.; by: intimately contactingzf; thet glycoliwthaain'orfoxygena andfamaqueousscaustica soluti'omat-,or examp1e;;371 'C (700."150 fortune.;4 hour; disclosed` in the.` various; processes; for;d

r converting:therchloridesto thefacidsa.- There-sultanA ing-...product will; be ai. mixture; of.` .para-toluic,I

acid `and.I terephthalc; acid which.` can bef sepa?-` ratedi. inl any suitable manner asv by distillation. Iii` desi-redl` `thepara-toluic; acid` may.: be;` passed 1.01 toi` atvchlorination .stageA for conversion: to l' paral-E ationtofftoluene or of. benzyl chloride (produced chloromethyl .benzoic.acidafterrwhichra' caustic; by chlorination of toluene c'ontainedinoradded oxidation"` Willa. serve toH forni terephthalic.i` acid. toi'thexylene` feed). has beenshovvn in the de-4 therefrom;` s'criptions'of the fiovv sheet' of` Fig. 1. This type Xylyl: chloride` isY obtained; from: toluene;` ofreactionwill berillustratedin connection'with 1.5: chloromethylationain"amanneranalogous tothe; the chloromethylatiori ofy benzyl chlcri'deto form elvilorornethylation` of" benzyl;l chloride: Excma para-xylylene dichloride. The reaction pla-ry.:conditionsaare.: Y i Y CHZCI CH2 ntrineneudicmoriae, m1: 50c LII 20. Toluene. niels.. Ho=o Hol H20 Zinelchloride; gr;,j `68"- Pa'r'armaltlehyd,)equivalents "1' CHZCI HCl` gasbubbled through" for 8ho1`1rsa`t*5" C.; I d ,5. th f d gt, Reactionmix allowed to standlovernight; washed; 1S' .0151 m e pseiceg da con nsafn w driedg.` andltered'l Reaction products' sepa @a a ys .suc is 2111.0 C Orl .ef Y rogen uw e' M rated.by'fracuonardistillation atreduced pres;l or aluminum chloride. The tendency of benzyl sure l chloride to react with itself may be reduced by i feeding the benzyl chlorideto an excess ofthe The-resulting product may convertedA to .tolui reaction mixture and by suchotherexpediente acids as hereinbeforedisclosedl as `will occurfto those skilled in the art. 30 From the foregoing` it. willi' becomfefapparentl` The process is illustrated'by` small scale ex` that the combination of pIOCeSSfStGDS-hlein dSrf amples in which benzyl chloride, formaldehyde, closed affords a method' for. obtaining substancatalyst,l and solvent were mixed and contacted tially complete conversion` of a, xylene; toluene.`

' WithHCl for a period of several hours. The reor analogous methyl-substituted"aromatic hydroaction mixturewas allowed to stand overnight, 35 carbon tow corresponding carboxylic acids.` 'with Washed, dried and ltered; Solvent and` un high yieldsjwhile avoidingfthenecessity for. comireacted benzyl chloride were removed by distillaplete chlorination to theoretical'. dichlorideicontion and the dichloride was recovered by-crystaltent. Itlisf unnecessary t'o-obtainmaximumzyieldf lization. Data and results of these runs are ofI the xylylene'fdichloridmforfexarnple; in: order given in Table X1: 40 toproduce dicarboxylic acidsitherebylpermitting' TABLE x1 Data from chloromethylation experiments Sample No. 22 23 24 A25` Reactauts: A

genzylgllilloide no1...f.f..h.. ilnols...f.... mol .f. lo of o e Oimal e y e" $11.9 or l (gissen. ginie. y (9310),. A `SoureeoflElCl anhydrousA anhydrous anhydrous fl25 ml.` conc.

Holi 1 m13 68H01' lz" ci" comilyn Po D1. I1 m 3 gtffffl ggoglimhyi sorgunil. Ethylsnoimrthyi `no gni. @Gianni ene Chlcrene Chlorene Chien Acetxc Acid. fr t o A e` so me; 5c 1de' l so 10e Tileiio: ::Ijijiiii: s t; s er.' Analysis of Product:2

Unreacted Benzyl Chloride, 11 92 percent. Xylylene Dichloride, per- 36 36 2 l cent.`

Polymers and Di-chloro- 27 25 42 Nil methylated Products,

percent.

1 Catalyst prepared by fusing 2l() gm. of ZnCh and stirringgin 10 gm. of lilCltas it cooled.`

2 Yields are based on the amount of formaldehydeused.

The xylylene dichloride may be converted to corresponding phthalic acid by either a single stage caustic oxidation or by first hydrolyzing to form the xylylene glycol and' then oxidizing to the dicarboxylic acid. Although a single stage conversion usually is preferred,l conditions `for a two-stage process will be illustrated. In the rst stage xylylene di'chlcride is subjected to hydrolysis in dilute Water solution at refluxing tem-` perature. The xylylene` glycol is recovered `by ether extractionof the reaction solution. In the second stage 'the recovered glycol is subjected to 75 tion chlorine content, production of corre- 19` spending carboxylic acid salts vmay be effected in single `stage conversions. The process also is adapted to produce polycarboxylic acids from the under-chlorinated compounds by further chlorination and conversion of any monocarboxylic acids from the foregoing single stage conversions. The process enables economicalutilization of byproduct HC1 produced in the chlorination reactions. It is important thatterephthalic and the likeacids are obtained by this invention Withrelatively cheap bulk chemicals, such as caustic soda, chlorine and, when desired, formaldehyde.

The beneiits of various features of this invention'are applicable tothe caustic oxidation of benzyl chloride, benzyl alcohol or benzaldehyde to benzoic acid. This is especially true concerning the use of air or gaseous oxygen to increase the yield of acid produced. For example, in comparing runs made at 371 C. (700 FJ, 3800 pounds per square inch, and Va reaction time of one hour, it. was found that by utilizing two mols of caustic in 8% aqueous solution per mol of benzyl chloride Without addition of air or oxygen, about 88% yield of ybenzoic acid was obtained with about 8% cy-product. vIn a second run at 371 C. (700 F.) at the same pressure and reaction time, the results were as follows:

Benzyl chloride reacted, mols 0.107 NaOH used, mols 0.225 Solution strength percent g 2 Mols of'Oz (as air)V 0.12 Mol'yield of 'acids per cent 96 Mol yield of by-product per cent 4 Intimate contact of the gaseous oxygen with the liquid reactants was obtained by vigorous agitation. Itgwill be observed that the' presence of this roxidizing agent-reduced the amount of byproduct formed from about 8 vto4%, a factor of approximatelyv one-half.

The effect of temperature on caustic oxidation of benzyl chloride to benzoic acid is illustrated by the following discussion and data. Y

Fig. 3 reveals that reduction oitemperature below 340 C. (650 F.) decreases yield of acid but does not render the process inoperative. Optimum reaction temperature for conversion of benzyl chloride to benzoic acid is in the range of from 370-400 C. (700-750 F.)

When either benzyl alcohol or benzaldehyde was substituted for the benzyl chloride underl exactly the same reaction conditions as were used 1 for the benzyl chloride conversion, somewhat higher yields of the acid were obtained. Table XII gives data on such substitutions:

TABLE XII r Y (l Y (ld NaOH ie ic Mols Mols Solution, Benzoic By: Chalged NaOH Percent Acid, Product,

Percent Percent Charge Oxidized Benzyl alcohol l l Benz'aldehyde. l

s 93 4 i s 95 4 Suitable temperatu-res for conversionof benzaldehyde and benzyl alcohol to benzoic acid bythis These by-products may be recycled to main reaction zone inorder to suppress further formation thereof and'increase the yield of acid.

Reference has been made to the fact that when and if ring chlorination occurs as a side reaction, the desired carboxylic acid is nevertheless obtained. This factor is believed highly significant to the good yields and superior purity of the products herein obtained. Under theV caustic oxidation reaction conditions herein disclosed, the chlorine in the ring is removed and converted to HC1 initially, which is of course neutralized by the caustic yielding a desired carboxylic acid. Theremoval of such ring chlorine is illustrated in conversion of chlorobenzyl 'chloride to benzoic acid in which the following reaction occurs:

Analogous reactions occur with xylyl, xylal and xylylene chlorides containing chlorine in the ring as well as in the side chain.

This application is a division of our application iiled October 4, 1947, Serial No. 777,970, entitled Preparation of Aryl Carboxylic Acids,V now UrS'. Patent No. 2,563,820.

Although the caustic alkali herein utilized for purposes of illustration has been sodium hydroxide, other strong alkali hydroxides such as potassium hydroxide may be substituted therefor. Likewise, other modications and Variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and only such limitations should be imposed as are indicated in the appended claims.

'We claim:

l. A process for producing benzene mono-carboxylic acids which comprises intimately contactingra mixture of a mono-chloromethyl benzene containing not more than two chlorine atoms in the chloromethyl group and aqueous sodium hydroxide with a free oxygen-containing gas at a temperature in the range 300 to 400 C., the quantity of free oxygen-containing gas brought into intimate contact with the mixture being such that itsfree oxygen content is approximately equivalent to the monochloromethyl benzene content of the mixture.

2. A process for producing benzoic acid which comprises intimately contacting a mixture of benzyl chloride and aqueous sodium hydroxide with a free oxygen-containing gas at a temperature inthe range 370 yto 400 C., the quantity of free oxygen-containing gas brought into intimate contact with the mixture beingV such that its free oxygen content is approximately equivalent Vto the benzyl chloride content of the mixture.

3. A process for producing benzoic acid which comprises intimately contacting a mixture of benzal chloride and aqueous sodium hydroxide with a free oxygen-containing gas at a temperature in the range 300 to 400 C., the quantity of free oxygen-containing gas brought into intimate contact with the mixture being such that its free oxygen content is approximately equivalent to the benzal chloride content of the mixture.

4. A process for producing toluic acid which comprises intimately contacting' a mixture of xylyl chloride and aqueous sodium hydroxide with a free oxygen-containing gas at a temperature in the range300 to 400 C., the quantity of free oxygen-containing gas brought'into intimate contact with the mixture being such that its free oxygen content is approximately equivalent to the xylyl chloride content of the mixture.

5. A process for producing toluic acid which comprises intimately contacting a mixture of xylal chloride and aqueous sodium hydroxide with a free oxygen-containing gas at a temperature in the range 300 to 400 C., the quantity of free oxygen-containing gas brought into intimate contact with the mixture being such that its free oxygen content is approximately equivalent to the xylal chloride content of the mixture.

JOHN L. DARRAGH.

ROBERT J, 15,

REFERENCES CITED Y The following references are of record in the le of this patent:

UNITED STATES PA'I'ENTS Number Name Date 939,584 Barstow Nov. 9, 1909 1,332,028 Coblentz et al Feb. 24, 1920 1,968,300 Kyrides July 31, 1934 FOREIGN PATENTS Number Country Date 586,383 France Mar. 25, 1925 364,442 Germany Nov. 25, 1922 639,578 Germany v .:v l Dec. 8, 1936 

1. A PROCESS FOR PRODUCING BENZENE MONO-CARBOXYLIC ACIDS WHICH COMPRISES INTIMATELYL CONTACTING A MIXTURE OF A MONO-CHLOROMETHYL BENZENE CONTAINING NOT MORE THAN TWO CHLORINE ATOMS IN THE CHLOROMETHYL GROUP AND AQUEOUS SODIULM HYDROXIDE WITRH A FREE OXYGEN-CONTAINING FKGAS AT A TEMPERATURE IN THE RANGE 300 TO 400* C., THE QUANTITY OF FREE OXYGEN-CONTAINING GAS BROUGHT INT I NTIMATE CONTACT WITH THE MIXTURE BEING SUCH THAT ITAS FREE OXYGEN CONTENT IS APPROXIMATELY EQUIVALENT TO THE MONOCHLOROMETHYL BENENE CONTENT OF THE MIXTURE. 